The High Fastball

One thing that I’ve been thinking about for awhile now is if there is an opportunity for pitchers to have some success getting swinging strikes up in the zone, particularly with their fastballs. I first heard this idea this offseason from a scout who had mentioned that the Cubs game plan against Cole during the Wild Card game was to force Cole to keep his fastball down.

The first thing I wanted to do was see if there was a trend of swinging strike location on fastballs over the past few seasons. So, I extracted every swinging strike on fastballs from the 2013 to 2015 regular season.

So yes, guys mostly missed fastballs when they’re up over the past few years. Which makes sense, because if the velocity is high enough, that’s a tough pitch to get to. Maybe this trend has been going on for awhile, I don’t know…doesn’t particularly surprise me though.

How about swinging strikes on fastballs up in the zone since 2008 though? Has there been more in the recent years? I’m going to define “up in the zone” as >= (.66 * sz_top) for each individual batter, where sz_top = the top of the strike zone as defined by PitchF/X. I’ve only considered four seam and two seam fastballs in this particular case.

Based on this trend, I took a look at the counts that pitchers threw a fastball up and got a swinging strike. Here’s the breakdown:

This isn’t entirely surprising, as a pitcher can exploit a guy up in the zone when he’s most aggressive. If the velo is there and the ball is high enough in the zone, a pitcher can draw a swing on a pitch that’s not really that hittable on a hitter looking to do some damage on the first pitch, or in an action count like 0-1. What about the types of pitches that were thrown before these high fastballs, i.e., set-up pitches?

This is interesting to me. Over 7,000 fastballs up for a swinging strike were set up with a fastball beforehand. I would personally have guessed that you would want to set up most of these fastballs with an off speed or breaking pitch.

I wanted to take it one step further and look into how we can predict whether or not a batter will whiff given that he swings as a fastball up. To do this, I first found a z-score for each fastball up’s vertical movement (pfx_z) in the 2015 season, as well as the z-score for each fastball’s velocity. After finding these z-scores, I weighted them based on the correlation of qualified pitchers’ (45+ innings pitched) SS% on high fastballs to velocity (0.35 correlation), as well as vertical movement (0.17 correlation). Finally, I added these z-scores together, creating an arsenal score that would represent each pitches’ effectiveness based on velo and vertical movement. Using logistic regression, I came up with the following graph. As we can see, coupling good vertical movement along with good velocity can lead to a higher probability of a swing and a miss up in the zone.

Last, I wanted to find which pitchers were most effective when they threw up in the zone. Similar to before, I found each qualified pitchers’ average velocity and vertical movement on all pitches they threw up in the zone. I then converted their average velo and vertical movement into z-scores, multiplied these z-scores by their respective correlations, and added these scores to find an overall arsenal score that would represent a pitcher’s fastball effectiveness up in the zone based on his average velo and vertical movement when he threw a ball in that location. The pitchers with the top 25 arsenal scores are as follows: